The invention relates to an apparatus and method for retarding internal combustion engines, typically diesel engines, by releasing compressed gases from each cylinder through an exhaust valve a compression near the top dead centre position of a compression stroke during, and same time, opening the exhaust valve of a cylinder on an intake stroke.
Truckers commonly encounter the problem of slowing heavy trucks, usually diesel-powered trucks, on long downgrades. It is well known that excessive use of conventional brakes leads to premature break wear and to overheating of the brakes. Consequently, it is well known to slow trucks with diesel engines by compression release retarding devices. These devices operate by cracking open each exhaust valve just prior to top dead centre of each compression stroke with the fuel supply to the engine cut off. The compressed gases are then diverted into the exhaust manifold, instead of being retained in each cylinder, which would provide an undesirable rebound effect and cancel the braking effect of the compression stroke.
Patents have been issued for engine braking devices of this type, including the following United States patents assigned to Jacobs Manufacturing Company: U.S. Pat. Nos. 4,592,319; 4,339,787; 4,398,510; 4,473,047; 4,423,712; 4,395,884; 4,474,006; 4,485,780; 4,510,900 and 4,572,114.
There is also U.S. Pat. No. 4,655,178 issued to the present inventor.
In my own previous U.S. patent application Ser. No. 07/015,683 filed Feb. 17, 1987, there was disclosed the principle of opening an exhaust valve of a cylinder on the intake stroke while cracking open an exhaust valve near top dead centre of a compression stroke. This causes the gases from the cylinder on the compression stroke to be diverted into the cylinder on the intake stroke, thus increasing the charge received in each cylinder. When that same cylinder reaches the compression stroke, there is more charge in the cylinder, thereby increasing the braking effect as the gases are compressed. In that previous application, hydraulic means was employed to operatively engage all of the exhaust valves of a group of cylinders, such that all of the exhaust valves of that group of cylinders are opened simultaneously. The exhaust valve of a first cylinder is cracked open when the cylinder is near top dead centre of a compression stroke, the other two cylinders being on the intake stroke and exhaust stroke respectively.
It is also known to retard engines using an exhaust restrictor. Exhaust restriction in itself provides a braking effect by providing a back pressure when each cylinder is on the exhaust stroke.